“The investigations concern four men and four women who worked at the German concentration camp in Danzig,” lead investigator Jens Rommel told Spiegel.

The men worked as guards, while the women were employed as secretaries or telephone operators, and all were born between 1918 and 1923.

Investigators are also searching for further suspects who worked at Bergen-Belsen and Neuengamme concentration camps.

For decades German authorities did almost nothing to bring those who worked in concentration camps during the Nazi era to justice, after a federal court ruling in 1969 which stated that simply working in one of the camps did not constitute being an accomplice to murder.

But the legal basis for prosecuting former Nazis changed in 2011 with Germany’s landmark conviction of former death camp guard John Demjanjuk.

He was sentenced not for atrocities he was known to have committed, but on the basis that he served at the Sobibor camp in occupied Poland – for having been a cog in the Nazis’ killing machine.

Over the past 12 months, there has been a new impetus to efforts to put low level functionaries in the machinery of the Holocaust behind bars.

More than 70 years after the Second World War, Hanning, 94, was sentenced to five years’ imprisonment over his role at the Nazi-run camp in occupied Poland.

In the Gröning case, both the prosecution and the defence appealed the ruling which has now gone to the federal court.

“We are hoping for a clarification from the federal court on what the current legal view is on affiliation with a concentration camp,” Rommel told Spiegel, adding that he hoped the court would overturn the 1969 ruling.